They nest in cavities, especially holes in trees, which are also favoured sites for endangered native hihi (stitchbirds) and kingfishers. Luckily, the rosellas are too big to fit into the nestboxes most hihi are using.
Perhaps the worst possible problem is disease. Parrots host a range of diseases and the presence of rosellas could be a limiting factor if native kakariki parrots were to be reintroduced to Bushy Park.
Eastern rosellas are native to the entire eastern coast of Australia, from Cape York to Tasmania.
"They're marvellous things in Australia, but they seem completely out of place somewhere like Bushy Park," Mr Frost said.